Rear wheel sprocket arrangement for a bicycle

ABSTRACT

A rear wheel sprocket arrangement for a bicycle comprises a plurality of sprockets comprising at least seven (7) coaxially arranged sprockets having different numbers of teeth, wherein an entire gear range of the sprocket arrangement is at least three-hundred fifty percent (350%), and wherein an average percentage gear stage step lies within a range of fifteen percent (15%) to thirty percent (30%).

This application claims priority to, and/or the benefit of, Germanpatent application DE 10 2015 210 503.2, filed on Jun. 9, 2015.

BACKGROUND OF THE INVENTION

The present invention relates to a rear wheel sprocket arrangement for abicycle, to a drive assembly for a bicycle with such a rear wheelsprocket arrangement, and to a bicycle with such a rear wheel sprocketarrangement or/and with such a drive assembly.

U.S. Pat. No. 3,748,916 A belonging to Morse is considered to be theclosest prior art. This patent discloses a rear wheel sprocketarrangement with an extremely large gear range of 500%, which isproduced by a total of five (5) coaxially arranged sprockets, namelyhaving the following numbers of teeth: nine (9), fourteen (14), twenty(20), thirty (30), and forty-five (45). The gear range is also referredto as the “gear ratio range” or, in view of the transmission of torquebrought about therewith, as the “torque range” or “torque ratio range”.The gear range is the ratio of the number of teeth of the largestsprocket to that of the smallest sprocket.

The individual percentage gear stage steps are very large in this knownrear wheel sprocket arrangement, which results in clearly perceptibleload jumps for the cyclist using the sprocket arrangement. In thepresent application, an “individual percentage gear stage step” isunderstood as meaning the difference in the numbers of teeth of axiallydirectly adjacent sprockets, divided by the number of teeth of thesmaller of the adjacent sprockets. The individual percentage gear stagesteps of the sprocket arrangement known from U.S. Pat. No. 3,748,916A—these are in total four (4) gear stage steps in five (5) sprockets—areaccordingly 55.6%, 42.9%, 50% and 50% from the smallest sprocket to thelargest sprocket. In terms of the arithmetic mean, i.e. the total sum ofthe individual percentage gear stage steps divided by the number of gearstage steps present, the average percentage gear stage step calculatedin this manner is 49.6%, i.e. only slightly less than 50%.

Furthermore, the prior art discloses rear wheel sprocket arrangementswhich have a larger number of sprockets and, associated therewith, asmaller average percentage gear stage step, in particular because saidknown rear wheel sprocket arrangements have a considerably smaller gearrange despite their larger number of sprockets.

EP 2 048 075 A discloses a rear wheel sprocket arrangement having atotal of nine (9) sprockets, the sprockets of which have the followingnumbers of teeth: eleven (11), thirteen (13), fifteen (15), seventeen(17), twenty (20), twenty-three (23), twenty-six (26), thirty (30), andthirty-four (34). This sprocket arrangement therefore has a gear rangeof approximately 309% with an average percentage gear stage step of15.2%.

As a further example of the prior art, reference should be made to atwelve (12) sprocket arrangement which is known from EP 2 022 712 A.This can have, for example, sprockets having the following numbers ofteeth: eleven (11), twelve (12), thirteen (13), fourteen (14), fifteen(15), seventeen (17), eighteen (18), nineteen (19), twenty-one (21),twenty-three (23), twenty-five (25), and twenty-seven (27). Thissprocket arrangement has a gear range of approximately 245.5% with anaverage percentage gear stage step of only 8.5%.

These known rear wheel sprocket arrangements no longer always meetmodern demands imposed thereon. New demands imposed on sprocketarrangements arise, firstly, from the tendency to reduce the number offront chainrings on the bicycle, optionally even to use just one (1)single chainring, and from the tendency to equip bicycles with electricauxiliary motors. The last-mentioned bicycles are currently generallyreferred to as pedelecs.

In particular the technical and legal frameworks for the operation ofpedelecs, the drives of which are assisted by electric motors, result indemands being imposed on rear wheel sprocket arrangements relating to alarge gear range and a comparatively moderate spacing between theindividual sprockets in order not to overload the cyclist by torquejumps possibly occurring when changing gear. Furthermore, it should benoted that electric auxiliary motors, also referred to here as“assisting electric motors”, may each generally output its assistingtorque only until a predetermined bicycle speed or a predeterminedbicycle speed range is reached. At higher speeds, the cyclist is reliantsolely on his muscle power.

In the case of what are referred to as pedelecs, there are substantiallyhigher continuous and peak loads acting on the rear wheel sprocketarrangement than in the case of bicycles operated solely by musclepower. The gear changing behavior on the bicycle also changes because ofthe higher power which is available owing to the assisting motor torque.In the case of conventional bicycles driven solely by muscle power,generally the change from one sprocket of the sprocket arrangement to anaxially adjacent sprocket is not made under load or only under a smallload. However, in the case of bicycles assisted by an electric motor thechange is frequently made, in particular from a sprocket to the nextsmaller sprocket, under full motor load, i.e. during an accelerationoperation. It should be noted here that, in the case of modern pedelecs,the assisting torque output by the electric motor is transmitted, likethe muscle power of the cyclist, to the rear wheel of the bicycle viathe rear wheel sprocket arrangement. Owing to the high overall torqueavailable in the case of pedelecs from the combination of the torquebased on muscle power and the assisting torque of the electric motor,specifically in the low speed range—depending on regulations, assistingthe muscle power of the cyclist by an electric motor is usuallypermitted up to a travel speed of between twenty (20) and thirty (30)kilometers per hour—such high acceleration values can be obtained thatundesirable, what are referred to as “multiple gear changing operations”occur, in which a temporally following gear changing operation isinitiated before the temporally preceding gear changing operation at therear wheel sprocket arrangement is finished.

Further changed demands emerge when the number of front chainrings isreduced since the torque transmission range of the bicycle then has tobe increasingly provided by the rear wheel sprocket arrangement. Thisgoes so far that, in the case of a single front chainring, the entiretorque transmission range which is available depends solely on theconfiguration of the rear wheel sprocket arrangement.

The reduction in the number of chainrings also may lead tocross-chaining situations of the bicycle chain running between thechainring or the chainrings and the rear wheel sprocket arrangementduring operation.

SUMMARY

It is the object of the present invention to develop known rear wheelsprocket arrangements for a bicycle in such a manner that they canbetter comply with the demands mentioned above than prior art rear wheelsprocket arrangements can.

This object is achieved according to the present invention by a rearwheel sprocket arrangement for a bicycle, comprising a plurality ofsprockets comprising at least seven (7) coaxially arranged sprocketshaving different numbers of teeth, wherein an entire gear range of thesprocket arrangement is at least 350%, and wherein an average percentagegear stage step lies within a range of 15% to 30%.

An individual percentage gear stage step is defined as the difference inthe numbers of teeth of two (2) axially directly adjacent sprocketsdivided by the number of teeth of the smaller of the adjacent sprockets.The average percentage gear stage step of the rear wheel sprocketarrangement is defined as the total sum of the individual percentagegear stage steps divided by the number of gear stage steps. A sprocketarrangement with k sprockets having different numbers of teeth in eachcase has k−1 gear stage steps.

The entire gear range of the sprocket arrangement is defined as theratio of the number of teeth of the largest sprocket to the number ofteeth of the smallest sprocket. Alternatively, the entire gear range ofthe sprocket arrangement may be at least 400% or at least 435%.Alternatively, t he average percentage gear stage step may lay within arange of 20% to 30%.

By means of the stated minimum gear range of at least 350%, the rearwheel sprocket arrangement of the present invention can transmit atorque, which is introduced at the pedal crank of a bicycle and istransmitted by the bicycle chain running between chainring and sprocketarrangement to the rear wheel sprocket arrangement, within a wide range.Therefore, both when the number of front chainrings is reduced and whenan assisting torque is optionally introduced by an electric motor inaddition to the muscle power supplied by the cyclist, a torqueappropriate to the respective cycling situation can be transmitted tothe rear wheel of a bicycle via the rear wheel sprocket arrangement. Atorque introduced at the pedal crank, and therefore at the frontchainring, can thus be stepped down to the rear wheel sprocketarrangement “to fast mode” or “to weak mode” or—for example whentravelling uphill—can be stepped up “to slow mode” or “to strong mode”.

With an average percentage gear stage step falling within a range of 15%to 30%, preferably even of 17%, 18% or 20% to 30%, although the averagegear stage step is larger than in the case of known sprocketarrangements with a large number of sprockets, it is significantlysmaller than in the case of known sprocket arrangements with a largegear range. Therefore, during the operation of the sprocket arrangement,when a change is made from one sprocket to an axially adjacent sprocket,undesirably large torque jumps are avoided. At the same time, with anumber of sprockets of already at least seven (7) coaxially arrangedsprockets, the outlay on installation and the construction spacerequired by the sprocket arrangement can advantageously be kept withinlimits.

When the proposed rear wheel sprocket arrangement is used on pedelecs,the problem of the “multiple gear changing operations” is also avoided.By means of the proposed spacing of the rear wheel sprocket arrangementwith reference to the stated range of values for the average percentagegear stage step, not only is an excessive torque jump which would beperceptible during gear changing avoided, but also the distance betweentransmission ratios of axially directly adjacent sprockets is increasedto such an extent that, when commercially available assisting electricmotors are used, even if a high torque is introduced into the pedalcrank shaft, there is a sufficiently large temporal interval between two(2) successive gear changing operations that the temporally precedingone of the two (2) gear changing operations can be completed before thegear changing operation temporally following the first one is initiated.

In order to avoid excessively large differences in the individual gearstage steps, it is advantageous if the values of the individualpercentage gear stage steps lie within a range of 15% to 35%, i.e. noindividual percentage gear stage step is smaller than 15% and none isgreater than 35%. Therefore, a certain variability of the individualpercentage gear stage steps is possible within the predetermined limits,and therefore, depending on the respectively selected gear stage, a stepof different size to the next smaller or to the next larger gear stagecan be provided. By this means, different torque demands in differentriding situations can be taken into consideration. Overall, however, asuniform a change as possible of the transmission ratio via the gearstages of the rear wheel sprocket arrangement is perceived by thecyclist riding a bicycle having the rear wheel sprocket arrangementaccording to the invention.

Furthermore, in order to be able to take account of the above-mentioneddifferent torque demands of different riding situations, it may beconceived of to adjust the individual percentage gear stage stepsbetween axially directly adjacent sprockets in a targeted manner. It maythus be conceived for the rear wheel sprocket arrangement to comprise agroup of successive axially adjacent sprockets which becomeprogressively larger and between which the values of axially successiveindividual percentage gear stage steps—when viewing in an axialdirection from the smallest sprocket towards the largestsprocket—increase from one gear stage to the next larger one. Duringgear changing through this group in the direction of the largestsprocket, it is therefore possible for a large torque transmission rangeto be passed through, with the percentage changes in the transmissionratio becoming ever larger as the sprockets become larger. For example,when gear changing downward (i.e. a gear changing operation to asprocket with a greater number of teeth), a gear change can beincreasingly rapidly made “to slow mode” or “to strong mode”. Such agear stage range can be superbly used as an acceleration range for themotor-assisted acceleration of a bicycle.

Similarly, the rear wheel sprocket arrangement can comprise a group ofaxially successive sprockets which become degressively larger andbetween which the values of axially successive individual percentagegear stage steps—when viewed in an axial direction from the smallestsprocket towards the largest sprocket—decrease from one gear stage tothe next. In this case, the percentage changes in the transmission ratiowhen gear changing through said group in the direction of sprocketsbecoming larger therefore become ever smaller. A group with sprocketsbecoming degressively larger can be used particularly for those gearstage ranges for which a portion of muscle driving power—increased incomparison to other gear stage ranges—is anticipated.

It should be clarified at this juncture that a sprocket can belong toboth groups mentioned. This is the case, for example, for boundarysprockets, and therefore a largest sprocket of the one group may be thesmallest sprocket of the other group in each case.

The rear wheel sprocket arrangement preferably has two (2) groups ofaxially successive sprockets which become degressively larger, wherein,furthermore preferably, the above mentioned group of axially successivesprockets which become progressively larger is placed axially betweentwo (2) groups of axially successive sprockets which become degressivelylarger. As before, the reference direction here is the axial directionfrom the smallest sprocket towards the largest sprocket.

A gear stage range which becomes degressively larger can therefore beplaced in the region of the smallest sprockets, for example the smallesttwo (2) or three (3) sprockets, since, when riding in these “rapid”gears, only a reduced, if any, assisting of the cyclist by the electricmotor generally takes place because of the previously explained limitingof the motor assisting to speeds below a predetermined limit speed. Inthese gear stages, the cyclist is predominantly dependent on his musclepower. For ergonomic reasons, it is advantageous, wherever the driver isdependent predominantly on muscle power in order to achieve propulsion,if the gear stage steps are selected to be smaller than wherever thefull assisting by the electric motor is available.

Surprisingly, it may also be expedient to configure the entirely “slow”gears, i.e. the gears having the largest sprockets, for example the two(2) or three (3) largest sprockets of the sprocket arrangement, as agear stage range which becomes degressively larger. These gear stagesundoubtedly do indeed provide a transmission ratio at which, underotherwise customary operating conditions, a speed of the bicycle shouldbe anticipated that lies below the limit value and for which completeassisting of the cyclist by electric motor is permissible. However,these gear stages are generally “hill gears” which are selected whentravelling on ascents (“travel uphill”) and in which a high drivingtorque and therefore a high driving power are also requested over aprolonged period.

As a rule, for the assisting of the cyclist by electric motor, there isa limit to the continuous power which is output by the assistingelectric motor. Said continuous power may indeed be exceeded for a shorttime in order rapidly to cope with a short, but high load demand.However, if the journey on an ascent lasts for a longer period—forexample for a period of more than thirty (30) or sixty (60) seconds—theassisting electric motor can only output the legally permittedcontinuous power, and therefore an increased portion of muscle drivingpower should be anticipated even for this load situation.

The gear stage range which becomes progressively larger can thereforeadvantageously be placed between the two (2) above-described gear stageranges which become degressively larger.

In order to be able to achieve especially high acceleration values inthe low speed range, which is advantageous in particular for the abovementioned pedelecs since, in these, the assisting electric motor mayoutput its torque only up to a predetermined limit speed of the bicycle,it is advantageous if the largest individual percentage gear stage stepoccurs between sprockets which are assigned to the speed range in whicha torque assistance by the electric motor is permitted. This is becausethe large individual percentage gear stage step then does not need to beovercome solely by muscle power—although this is readily possible whenthe above mentioned conditions are maintained. Since rear wheel sprocketarrangements are always used on a bicycle together with at least one (1)front chainring, a bicycle speed or at least a bicycle speed range canreadily be assigned to each sprocket of the sprocket arrangement, takinginto consideration the possible chainrings and rear wheels and alsoassuming a power which can customarily be output by a cyclist,optionally with assisting by the electric motor. It is thereforeparticularly advantageous for the above mentioned reasons that thelargest individual percentage gear stage step occurs between the thirdlargest sprocket and the fourth largest sprocket or/and between thefourth largest sprocket and the fifth largest sprocket. It may also beconceived here—and this is even preferred in the present case—that thetwo (2) individual percentage gear stage steps between the third largestsprocket and the fourth largest sprocket and between the fourth largestsprocket and the fifth largest sprocket are identical in size. Thelatter is preferred in particular for a sprocket arrangement havingprecisely eight (8) sprockets.

In order to ensure the desired large gear range while avoiding asimultaneously high loading of the bicycle chain, the largest sprocketcan have more than forty (40) teeth, for example at least forty-four(44) teeth, preferably at least forty-eight (48) teeth. As will also beshown further below, forty-eight (48) teeth are preferred for thelargest sprocket as compared to forty-four (44) teeth since the numberforty-eight (48) has more integral factors than the number forty-four(44). This is advantageous for the precise sequence of gear changingoperations towards this sprocket. Similarly, the smallest sprocket canhave at least ten (10), preferably at least eleven (11) teeth. In ordernot to unnecessarily restrict the gear range which can be achieved withthe sprocket arrangement, the smallest sprocket should not have morethan thirteen (13) teeth.

In order to ensure precise gear changing operations between individualsprockets, it is advantageous if the number of teeth of each of the four(4) largest sprockets of the rear wheel sprocket arrangement is anintegral multiple of four (4). In order to achieve the values of theabove mentioned individual percentage gear stage steps specifically inthe case of the largest sprockets, it is preferred, however, if thenumber of teeth is an integral multiple of eight (8). In this case, itis possible to reach the situation, which is advantageous for achievingextremely precise gear changing operations, in which the numbers ofteeth of axially directly adjacent sprockets—here of the four (4)largest sprockets—can be divided by the difference in the numbers ofteeth of the axially directly adjacent sprockets.

However, for the smaller sprockets, other conditions generally have toapply than for the previously mentioned four (4) largest sprockets. Ifthe above mentioned steps of eight (8) were continued here, theindividual percentage gear stage steps towards the smallest sprocketwould become undesirably large. This can be avoided by the number ofteeth of each of three (3) sprockets from a group of four (4) axiallysuccessive sprockets, wherein this group comprises the sprockets fromthe fourth largest to the seventh largest sprocket, being an integralmultiple of three (3), even better an integral multiple of six (6). Itshould be clarified that the fourth largest sprocket preferably meetsall of the above mentioned conditions, for example if it comprisestwenty-four (24) teeth, and therefore its number of teeth can be dividedby eight (8), six (6), four (4), and three (3).

For the above mentioned reasons of as precise a gear changing behavioras possible, according to an advantageous development of the inventionthe rear wheel sprocket arrangement has at least five (5) sprockets,preferably at least six (6) sprockets, for which the followingdivisibility condition applies that the numbers of teeth of two (2)axially directly adjacent sprockets can each be divided by thedifference in said numbers of teeth without a remainder. This preferablyinvolves the five (5), preferably six (6), largest sprockets of thesprocket arrangement. Whenever the sprocket arrangement has a total ofprecisely seven (7) sprockets, it can have precisely five (5) sprocketsfor which the divisibility condition mentioned is met. In the case of asprocket arrangement having a total of precisely eight (8) sprockets,said sprocket arrangement can have precisely six (6) sprockets for whichthe divisibility condition mentioned is met.

The use of a rear wheel sprocket arrangement having at least seven (7)sprockets has the advantage that the largest sprocket does notnecessarily have to be cupped or otherwise formed such as with a bentcross section. There is sufficient construction space in order toprovide the largest sprocket as a generally planar sprocket. By thismeans, even the particularly loaded largest sprocket can withstand thechain loads that are higher during assistance by the electric motorbecause of the higher available torque without thereby having to acceptweight disadvantages, for example because of additional stiffening meansand the like.

The largest sprocket is preferably not itself directly designed fortransmitting torque to the bicycle rear wheel axle. This preferablytakes place by means of a driver which is coupled in a manner known perse to the bicycle rear wheel axle. The largest sprocket is preferablyalso not itself designed directly for transmitting torque to the driver.Instead, it is provided that the largest sprocket has a central openingthrough which the driver passes, wherein there is no direct form-fittingengagement between the largest sprocket itself and the driver fortransmitting torque between the largest sprocket and the driver.

Torque can be transmitted between the largest sprocket and a driver byan adapter element which is arranged in the torque transmission pathbetween the largest sprocket and the driver. The largest sprocket cantherefore be coupled to a driver by an adapter element for thetransmission of torque, wherein the adapter element is preferably placedon that side of the largest sprocket which faces away from the rest ofthe sprockets. The one (1) driver mentioned here could be the drivermentioned in the previous paragraph. Although it is conceivable for theadapter element to be placed only partially on that side of the largestsprocket which faces away from the smaller sprockets, it is preferredfor the adapter element to be placed entirely on this side. By thismeans, it is possible to arrange the entire rear wheel sprocketarrangement on a bicycle at a larger axial distance from thelongitudinal center plane of the bicycle than if the adapter elementwere arranged axially within the sprocket arrangement. By this means,the chain skew can be reduced especially in the case of engagement ofthe chain with the large sprockets. The large sprockets, because oftheir large diameter, are most highly loaded by chain skew and, becauseof their size, have a greater buckling tendency than the smallersprockets of the sprocket arrangement.

In order to facilitate manufacturing and installation and in order toobtain as great a stability and rigidity of the sprocket arrangement aspossible, it can be provided that a plurality of sprockets is formed asa single-piece sprocket component within the rear wheel sprocketarrangement. The entire rear wheel sprocket arrangement can in principlebe designed as a single-piece sprocket component although this is notpreferred. The largest sprocket is preferably designed as a separateindividual sprocket, for example in order to be able to select asuitable material for this sprocket, in which the greatest torque istransmitted to the bicycle rear wheel, irrespective of the material ofother sprockets of the sprocket arrangement. The largest sprocket canalso, as an individual sprocket for the transmission of torque, bedirectly connected to the second largest sprocket which is axiallyadjacent thereto. This is generally indeed the case for as effective atransmission of torque as possible.

The smallest sprocket of the sprocket arrangement can also be formedseparately as an individual sprocket in order to make said sprocketeasily exchangeable. By this means, highly loaded, worn or deformedsprockets can easily be replaced, or torque transmission ratios can beadapted to changed demands by exchanging sprockets.

The aspect of the design as an individual sprocket for easierexchangeability preferably applies to that sprocket with which, assumingcustomary pedal frequencies within a range of sixty-five (65) toseventy-five (75) revolutions per minute and taking into considerationthe known chainring and the known rear wheel of a bicycle, a ridingspeed is achieved which corresponds to the above-described assistinglimit speed, above which assisting of the cyclist by the electric motoris impermissible. Observations have shown that cyclists of pedelecs liketo exhaust the scope of the assistance by the electric motor that istechnically available to them, but do not generally attempt to gotherebeyond by using their own muscle power. In this respect, in thecase of pedelecs, an over-averagely high stressing of said sprocketassigned to the assisting speed limit should be anticipated.Particularly this sprocket is therefore preferably configured as anexchangeable individual sprocket. This is in many cases the sixthlargest sprocket of the sprocket arrangement. Depending on the totalnumber of sprockets of the sprocket arrangement, this sprocket can alsobe the fifth largest sprocket or the seventh largest sprocket.

Preferably at least three (3), particularly preferably at least four(4), most preferably precisely four (4) sprockets of the rear wheelsprocket arrangement are therefore designed as a single-piece sprocketcomponent within the rear wheel sprocket arrangement. The single-piecesprocket component preferably contains the second largest sprocket. Bycontrast, the second smallest sprocket, possibly also the third smallestsprocket, is preferably provided as an individual sprocket which isformed separately in order to facilitate the exchange thereof.

Alternatively or additionally to the single-piece design of a pluralityof sprockets, a plurality of sprockets, in particular in each case two(2) axially directly adjacent sprockets, can also be directly connectedto each other by connecting means, such as, for example, pins, rivets,screws, or any combination thereof. In order to achieve as high arigidity as possible, the connecting means are provided radially in theregion of the outermost 50% of the radial extent of the smaller of two(2) sprockets, which are directly connected to each other, between saidsprockets, preferably in the region of the outermost 33%, particularlypreferably in the region of the outermost 25%, most preferably in theregion of the outermost 20% of the radial extent of the smaller of thetwo (2) sprockets which are connected directly to each other. Theconnecting means can be formed integrally with one (1) of the two (2)directly connected sprockets, preferably with the smaller sprocket. Theconnecting means are designed for transmitting torque about the commonsprocket axis, preferably also for transmitting axial force along thesprocket axis. In order to achieve as stable a connection as possibleradially as far as possible on the outside, the connecting means can beconnected to the smaller of two (2) sprockets, which are directlyaxially adjacent and are connected to each other, in the region of theroots of the teeth thereof.

The preferred radial regions, which are mentioned for the connectingmeans, for the attachment of the latter to or between a pair of axiallydirectly adjacent sprockets also apply to the design of a directsingle-piece connection of two (2) axially directly adjacent sprocketsto each other.

While it was stated at the beginning that the rear wheel sprocketarrangement comprises at least seven (7) sprockets, the rear wheelsprocket arrangement may, of course, also comprise significantly morethan seven (7) sprockets. However, this is not at all necessary in orderto realize the desired large gear range with the above mentioned averagepercentage spacing. The rear wheel sprocket arrangement advantageouslycomprises precisely seven (7) or precisely eight (8) or precisely nine(9) sprockets. Such a number of sprockets permits the above mentioneddesign of the largest sprocket as a generally planar sprocket having theabove mentioned advantages. The precise number of sprockets mentionedalso permits the above mentioned advantageous arrangement of the adapterelement axially outside the sprocket arrangement, i.e. on that side ofthe largest sprocket which faces away from the smaller sprocket, withthe above-described result of advantageously reduced chain skew at thelarger sprockets.

In principle, any chains can be used with the rear wheel sprocketarrangement. However, in order to achieve a small axial constructionspace demand of the sprocket arrangement, it is advantageous if a frontface distance between axially directly adjacent sprockets is between 4.2millimeters and 4.4 millimeters, preferably between 4.3 millimeters and4.4 millimeters, particularly preferably 4.35 millimeters. The “frontface distance” here is the distance between front faces of axiallydirectly adjacent sprockets, which front faces are orthogonal withrespect to the common axis of rotation of the sprockets, in a region ofthe sprocket body in the vicinity of a tooth on that side of thesprocket which faces towards the smaller sprocket in each case or awayfrom the larger sprocket in each case. One skilled in the artunderstands the term “front face” since the position of the rear ratchetmechanism of a derailleur is aligned with said face. The “front face” isgenerally the face on the sprocket side which, in the mounted state,faces away from the longitudinal center plane of the bicycle, and onwhich face a sprocket, disregarding any axially protruding teeth whichare present and any projections which are present in the vicinity of thehub, rests on a flat underlying surface.

The bicycle chain interacting with the rear wheel sprocket arrangementshould be selected in accordance with the selected front face distance.

In the case of a seven (7) sprocket arrangement, the rear wheel sprocketarrangement according to the invention preferably has the followingspacing from the smallest sprocket towards the largest sprocket: twelve(12), fourteen (14), eighteen (18), twenty-four (24), thirty-two (32),forty (40), and forty-eight (48). By contrast, in the case of an eight(8) sprocket arrangement, the preferred spacing is as follows: eleven(11), thirteen (13), fifteen (15), eighteen (18), twenty-four (24),thirty-two (32), forty (40), and forty-eight (48).

According to a further aspect of the present invention, the presentapplication relates to a rear wheel sprocket arrangement for a bicycle,comprising at least seven (7) coaxially arranged sprockets havingdifferent numbers of teeth, wherein the entire gear range of thesprocket arrangement—defined as the ratio of the number of teeth of thelargest sprocket to the number of teeth of the smallest sprocket—is atleast 350%, preferably at least 400%, particularly preferably at least435%.

The present invention furthermore relates to a drive assembly for abicycle having a rear wheel sprocket arrangement, as described above,and having a front chainring, wherein the number of teeth of the frontchainring is smaller than the number of teeth of the largest sprocketand larger than the number of teeth of the third largest sprocket. A“hill gear” making it possible to overcome even large ascents cantherefore be realized between the front chainring and the largestsprocket, while even as the chain is being placed onto the third largestsprocket, the torque is stepped down “to fast mode” or “to weak mode”.The chainring and the second largest sprocket can have the same numberof teeth here, and therefore, when the chain is placed onto the secondlargest sprocket, the torque introduced at the chainring is transmittedunchanged, apart from unavoidable friction losses, to the rear wheel.

Since the present rear wheel sprocket arrangement is specifically alsointended to meet demands which are imposed on a drive assembly for abicycle having precisely one (1) front chainring, the drive assemblypreferably comprises precisely one (1) front chainring. In the eventthat more than one (1) front chainring is present, the conditionsspecified in the preceding claim are intended to apply to the largestchainring.

The decisive factor here is intended to be the “effective number ofteeth” of the chainring, i.e. a number of teeth which arises taking intoconsideration a gearing possibly arranged between the location at whichtorque is introduced and the chainring and the transmission ratio ofsaid gearing. If, for example, between the location at which torque isintroduced and a chainring having only sixteen (16) teeth a gearing isprovided which increases the introduced torque towards the chainring bythe factor of 2.5, i.e. steps up said torque “to strong mode”—wherein,for reasons of maintaining energy, the rotational speed at which thetorque is introduced is reduced by the same factor—the chainring has aneffective number of teeth which is increased by 2.5 times; i.e. forty(40) teeth in this example.

Since the present rear wheel sprocket arrangement is particularlysuitable for the interaction with an electric motor assisting thecyclist, the drive assembly furthermore preferably comprises anassisting electric motor which is designed or/and is arranged in orderto transmit its assisting torque to the rear wheel via the rear wheelsprocket arrangement. The assisting electric motor can be coupled orcouplable here to the chainring in order to transmit torque. Forexample, the electric motor can be coupled or couplable to the pedalcrank shaft to which the pedal cranks actuated by the cyclist are alsocoupled. The coupling of the electric motor to the chainring or to thepedal crank shaft can take place by means of a gearing, for example aplanetary gearing.

The present invention finally relates to a bicycle having a rear wheelsprocket arrangement, as is described above, or/and having a driveassembly, as has previously been described.

BRIEF DESCRIPTION OF DRAWINGS

The present invention is explained in more detail below with referenceto the attached drawings, in which:

FIG. 1 is a roughly schematic side view of a bicycle which is equippedwith a drive assembly according to the invention using a rear wheelsprocket arrangement according to the invention (the rear wheel sprocketarrangement is merely indicated in a roughly schematic manner),

FIG. 2 shows a detailed longitudinal sectional view, which contains thecommon sprocket axis, of an embodiment according to the invention of arear wheel sprocket arrangement having eight (8) sprockets, and

FIG. 3 shows a perspective longitudinal sectional view of the sprocketarrangement of FIG. 1.

DETAILED DESCRIPTION

In FIG. 1, a bicycle provided with a sprocket arrangement according tothe invention is denoted in general by 10. A front wheel 12 and a rearwheel 14 are fastened to a bicycle frame 16 so as to be rotatable aboutrespective wheel axles which are orthogonal to the plane of the drawingof FIG. 1. The front wheel 12 can be connected to the bicycle frame 16via a sprung fork 18. The rear wheel 14 can also be connected to thebicycle frame 16 via a sprung suspension 20.

The rear wheel 14 is driveable via a drive assembly 22, comprising anindividual front chainring 24 and a rear wheel sprocket arrangement 26,which is merely illustrated in roughly schematic form in FIG. 1. Thedriving torque can be transmitted via pedal cranks 28 and a pedalcrankshaft 28 a, which is connected thereto, to the front chainring 24and from the latter by means of a bicycle chain 30 to the rear wheel 14via the rear wheel sprocket arrangement 26. In order to assist a cyclistdriving the pedal cranks 28 with muscle power, an assisting electricmotor 32 can be arranged on the bicycle frame 16 in such a manner thatthe latter also transmits its assisting driving torque to the frontchainring 24 via the pedal crankshaft 28 a. A gearing, in particularplanetary gearing, can be provided between the pedal crankshaft 28 a andthe chainring 24. The transmission ratio of the gearing should be takeninto consideration in the calculation of the effective number of teethof the chainring 24. The actual number of teeth of the chainring 24should be multiplied here by the factor with which the gearing transmitsa torque, which is introduced into said gearing, towards its outputside. An increase in the torque by means of the gearing therefore leadsto an effective number of teeth of the chainring 24 which is increasedin relation to the actual number of teeth, and vice versa.

A battery 34 as an energy accumulator for the assisting electric motor32 can be provided in or on the frame 16.

As FIGS. 2 and 3 show, the rear wheel sprocket arrangement 26 or elseonly the sprocket arrangement 26 has a plurality of sprockets whichincludes a series of coaxial sprockets of different numbers of teeth,wherein, in the mounted state of FIG. 1, the numbers of teeth decreasecontinuously towards the outside from the longitudinal center plane ofthe bicycle 10 that is parallel to the plane of the drawing of FIG. 1.

The bicycle chain 30 can be brought in a manner known per se by a rearderailleur 36 into meshing engagement with a sprocket which is to beselected by the cyclist from the plurality of sprockets of the sprocketarrangement 26 in order to transmit torque to the rear wheel 14. Thebicycle chain 30 is a roller chain which is known per se and as istypical for use on bicycles.

Both the muscle torque of the cyclist and the assisting torque of theelectric motor 32 are transmitted to the rear wheel 14 via the rearwheel sprocket arrangement 26 on the bicycle 10 in the example. Theelectric motor 32 therefore has the effect as though the cyclist couldtrigger a pedal power which is increased by the assisting power of theelectric motor 32.

Since the bicycle 10 shown by way of example has precisely one (1) frontchainring 24, the entire gear range of the bicycle 10 is realized by therear wheel sprocket arrangement 26. A longitudinal sectional viewthrough said sprocket arrangement 26 is shown in FIG. 2. FIG. 3 shows aperspective longitudinal sectional view through the sprocket arrangement26 of FIG. 2.

The sprocket arrangement 26 shown by way of example has eight (8)sprockets 38, 40, 42, 44, 46, 48, 50 and 52 which are arranged coaxiallywith respect to a common sprocket axis A. The sprocket axis A is alsothe axis of rotation of the rear wheel 14. The sprocket axis A isorthogonal with respect to the plane of the drawing of FIG. 1 and liesin the plane of the drawing of FIG. 2.

Of the sprockets 38 to 52 mentioned, the sprocket 38 is the largestsprocket and the sprocket 52 is the smallest sprocket.

In the present example, the largest sprocket 38, which is preferably ofa generally planar design, has forty-eight (48) teeth. The numbers ofteeth of the sprockets 40 to 52 are forty (40), thirty-two (32),twenty-four (24), eighteen (18), fifteen (15), thirteen (13), and eleven(11) in the sequence mentioned. The largest sprocket 38 is designed asan individual sprocket, as are the sprockets 48, 50 and 52. By contrast,the sprockets 40, 42, 44 and 46 are preferably designed as asingle-piece sprocket component or dome 54. The sprockets 48, 50 and 52can therefore be exchanged individually as required.

The sprockets 40 to 46 of the sprocket dome 54 are preferably connectedby webs 56, 58, 60 which are formed integrally with the respectivesprockets, which webs are in each case arranged between two (2) axiallydirectly adjacent sprockets. The webs 56 to 60 are provided here as farradially in the outside as possible in order to obtain a sprocket dome54 which is as stable and stiff as possible. Depending in each case onthe sprocket size, the webs lie in the radially outermost 15% to 25% ofthe radial region of extent of the smaller of the two (2) axiallyadjacent sprockets connected directly to each other, measured in eachcase from the sprocket axis A. The webs preferably end at the smaller ofthe two (2) directly connected sprockets in the region of a root of atooth.

Webs 62 are advantageously integrally formed on the largest sprocket 40of the sprocket dome 54, said webs protruding away from the largestsprocket in the direction of the smaller sprockets 42, 44 and 46 of thesprocket dome 54 and serving for the connection to the largest sprocket38. However, said webs are not integrally connected to the largestsprocket 38.

An alternative connection of the sprocket 40 to the largest sprocket 38is illustrated by way of example in the upper half of the image of FIG.2. A pin 64 which passes through the sprocket 38 can thus be integrallyformed as a single piece on the sprocket 40, on the side facing thelargest sprocket 38. Instead of a pin which is integrally formed on thesprocket 40, the pin 64 can also be formed separately from the sprockets38 and 40 which are connected by said pin, or the pin 64 can be formedintegrally on the sprocket 38, specifically on the side facing thesprocket 40, and can pass through the sprocket 40.

The integral connection of the sprockets 40 to 46 to one another inorder to form the sprocket dome 54 can be entirely or partially replacedby the illustrated or by the above-explained pin connection using thepin 64.

With the above mentioned spacing of the sprockets 38 to 52, the sprocketarrangement 26 has a gear range of forty-eight (48) divided by eleven(11), i.e. approximately 436.4%. The individual percentage gear stagesteps from the smallest sprocket 52 to the largest sprocket 38 arethirteen (13) minus eleven (11), divided by eleven (11), i.e.approximately 18.2%; fifteen (15) minus thirteen (13), divided bythirteen (13), i.e. approximately 15.4%; eighteen (18) minus fifteen(15), divided by fifteen (15), i.e. 20%; twenty-four (24) minus eighteen(18), divided by eighteen (18), i.e. approximately 33.3%; thirty-two(32) minus twenty-four (24), divided by twenty-four (24), i.e.approximately 33.3%; forty (40) minus thirty-two (32), divided bythirty-two (32), i.e. 25%; and forty-eight (48) minus forty (40),divided by forty (40), i.e. 20%. All of the gear stage steps thereforelie within a range of between 15.4% and 33.3%. It is therefore possibleto divide a large gear range relatively uniformly into similarlyrelatively few gear stages. At the same time, no gear stage step is ofsuch a size that, during a gear changing operation into a gear stage orout therefrom, the cyclist would perceive an unpleasantly large torquejump.

The arithmetic mean of the individual percentage gear stage stepscalculated above, i.e. the average percentage gear stage step, isapproximately 23.6% in the example illustrated.

The front chainring 24 advantageously has an effective number of teethof forty (40) teeth, which, in the case of the pedelec 10 which isillustrated here and is assisted by an electric motor, is customarilyachieved by a chainring having sixteen (16) teeth and a gearingconnected upstream and having an amplification of the torque by 2.5times from the location at which the torque is introduced towards thechainring 24.

If, in the case of the bicycle 10 illustrated by way of example, thestarting point is an entirely customary pedal frequency of sixty-five(65) revolutions per minute, then, using the particular rear wheel, asize of which is likewise known, together with the chain, a speed ofapproximately 7.5 kilometers per hour is achieved at the largestsprocket 38, a speed of approximately 9 kilometers per hour is achievedat the second largest sprocket 40, a speed of 11.2 kilometers per houris achieved at the third largest sprocket 42, a speed of approximately15 kilometers per hour is achieved at the fourth largest sprocket 44, aspeed of approximately 19.9 kilometers per hour is achieved at the fifthlargest sprocket 46, a speed of approximately 23.9 kilometers per houris achieved at the sixth largest sprocket 48, a speed of 27.6 kilometersper hour is achieved at the seventh largest sprocket 50, and a speed of32.6 kilometers per hour is achieved at the smallest sprocket 52.

Depending on the respective legal regulations, in the case of bicyclesassisted by electric motor an output of an assisting torque by theelectric motor is permitted only up to a predetermined speed limit. InGermany, for example, the cyclist is allowed to be assisted by the fulltorque of the assisting electric motor 32 only up to a speed oftwenty-five (25) kilometers per hour. At higher speeds, eitherassistance is no longer permitted or—at speeds slightly above the limitspeed of twenty five (25) kilometers per hour—only a partial assistanceis permitted by a partial torque which is reduced in comparison to thefull assisting torque.

In the case of the present rear wheel sprocket arrangement 26 of theexample illustrated, full assistance of the cyclist by the torque of theelectric motor 32, with the stated assumptions of a front chainring 24having an effective number of teeth of forty (40) and a pedal frequencyof sixty-five (65) revolutions per minute, is thus found only in gearstages which are formed by the six (6) largest sprockets 38 to 48. Inthe present case, the sprocket 48 is therefore the sprocket which isassigned to the assisting limit speed of twenty-five (25) kilometers perhour, for which particularly severe wear can be anticipated for thereasons mentioned in the introductory part of the description.

For the advantageous utilization of the greatest possible assistance ofthe cyclist by the assisting electric motor 32, the largest individualpercentage gear stage steps lie within this “assisting range” which isformed by the six (6) largest sprockets 38 to 48. The largest individualpercentage gear stage steps of in each case 33.3% advantageously liebetween the third largest and the fourth largest sprockets 42 and 44 andbetween the fourth largest and the fifth largest sprockets 44 and 46.The third largest individual percentage gear stage step of 25%(nominally actually the second largest individual percentage gear stagestep) is provided between the second largest and the third largestsprockets 40 and 42. By this means, high acceleration is achieved whilesimultaneously avoiding undesirable multiple gear changing operations.

The three (3) smallest sprockets 52, 50 and 48 form a first group ofsprockets which, when viewing in the axial direction from the smallestsprocket 52 towards the largest sprocket 38, become degressively larger.This means that the individual percentage gear stage steps placedbetween said sprockets 52 to 48 become smaller in the direction from thesmallest sprocket 52 towards the largest sprocket 38.

The three (3) successive axially adjacent sprockets 48, 46 and 44 form asecond group of sprockets which, when viewing in the axial directionfrom the smallest sprocket 52 towards the largest sprocket 38, becomeprogressively larger. This means that the individual percentage gearstage steps placed between the sprockets 48 to 44 become larger in thestated viewing direction.

The three (3) largest successive axially adjacent sprockets 42, 40 and38 form a third group of sprockets which, when viewing in the axialdirection from the smallest sprocket 52 towards the largest sprocket 38,became degressively larger. The individual percentage gear stage stepsplaced between the sprockets 42 to 38 become smaller in turn in thestated viewing direction.

The sprocket 48 belongs as a boundary sprocket both to the first and tothe second group.

For the sprockets 48 to 38, the particularly advantageous condition forprecise gear changing of the bicycle chain 30 from one sprocket of thesprockets 48 to 38 to an axially directly adjacent sprocket of thesprockets 48 to 38 applies that the numbers of teeth of each of two (2)axially directly adjacent sprockets can be divided by the difference inthe numbers of teeth thereof without a remainder.

The sprocket arrangement 26 is passed through axially by a driver 66.With said driver 66, the sprocket arrangement 26 is connected to therear wheel axle (not illustrated in FIGS. 2 and 3) of the rear wheel 14in the driving direction for the transmission of torque and by afreewheel in the direction counter to the driving direction.

The preferably generally planar largest sprocket 38 has, at its borderclosest to the sprocket axis A, an opening 68 through which the driver66 likewise passes. There is no direct torque transmission connectionbetween the largest sprocket 38 and the driver 66. Said torquetransmission connection is on the contrary only produced by an adapterelement 70 which is firstly connected to the largest sprocket 38 in atorque-transmitting manner and is secondly connected to the driver 66 ina torque-transmitting manner.

The adapter element 70 is provided on the rear side 38 b of the largestsprocket 38, which rear side faces away from the remaining sprockets 40to 52. This unusual arrangement of the adapter element 70 is firstlypossible because of the number of sprockets of a total of only eight (8)sprockets of the sprocket arrangement 26 and is secondly possiblebecause of the relatively small distance between the front faces 38 a,40 a, 42 a, 44 a, 46 a, 48 a, 50 a, and 52 a, which distance, in thepresent example, is between 4.2 millimeters and 4.4 millimeters, indetail is precisely 4.35 millimeters.

Owing to the number of sprockets of up to nine (9), precisely eight (8)in the example illustrated, with a simultaneously small front facedistance, the sprocket arrangement 26 requires so little axialconstruction space that the adapter element 70 can be arranged outsidethe construction space taken up axially by the sprocket arrangement 26.By this means, the sprocket arrangement 26, in particular the largestsprocket 38, which is particularly loaded by chain skew, can be arrangedaxially further away from the longitudinal centre plane of the bicycle10, and therefore the skew angle of the bicycle chain 30 relative to thelongitudinal centre plane of the bicycle 10 is smaller if said bicyclechain runs over the largest sprocket 38 than if the adapter element 70were arranged on the side of the front face 38 a of the largest sprocket38. As a result, the loading of the largest sprocket 38 which, becauseof its considerable diameter, exhibits an increased buckling tendencycan be considerably reduced during operation.

A spacer sleeve 72 which defines the axial distance of the largestsprocket 38 from the smallest sprocket 46 of the sprocket dome 54 isadvantageously arranged in order to axially support the largest sprocket38 in the vicinity of the driver 66.

While the present invention has been described above by reference tovarious embodiments, it should be understood that many changes andmodifications can be made to the described embodiments. It is thereforeintended that the foregoing description be regarded as illustrativerather than limiting, and that it be understood that all equivalentsand/or combinations of embodiments are intended to be included in thisdescription.

What is claimed:
 1. A rear wheel sprocket arrangement for a bicyclecomprising: a plurality of sprockets comprising at least seven (7)coaxially arranged sprockets having different numbers of teeth, whereinan entire gear range of the sprocket arrangement is at leastthree-hundred fifty percent (350%), and wherein an average percentagegear stage step lies within a range of fifteen percent (15%) to thirtypercent (30%).
 2. A rear wheel sprocket arrangement according to claim1, wherein the entire gear range of the sprocket arrangement is at leastfour-hundred percent (400%).
 3. A rear wheel sprocket arrangementaccording to claim 1, wherein the entire gear range of the sprocketarrangement is at least four-hundred thirty-five percent (435%).
 4. Arear wheel sprocket arrangement according to claim 1, wherein theaverage percentage gear stage step lies within a range of twenty percent(20%) to thirty percent (30%).
 5. A rear wheel sprocket arrangementaccording to claim 1, wherein values of individual percentage gear stagesteps lie within a range of fifteen percent (15%) to thirty-five percent(35%).
 6. A rear wheel sprocket arrangement according to claim 1,wherein the plurality of sprockets comprises, when viewing in an axialdirection from a smallest sprocket towards a largest sprocket, a groupof axially successive sprockets which become progressively larger, and agroup of axially successive sprockets which become degressively larger.7. A rear wheel sprocket arrangement according to claim 6, wherein thegroup of axially successive sprockets which become progressively largeris placed axially between two (2) groups of axially successive sprocketswhich become degressively larger.
 8. A rear wheel sprocket arrangementaccording to claim 7, wherein a largest individual percentage gear stagestep occurs between a third largest sprocket of the plurality ofsprockets and a fourth largest sprocket of the plurality of sprockets orbetween the fourth largest sprocket and a fifth largest sprocket of theplurality of sprockets.
 9. A rear wheel sprocket arrangement accordingto claim 7, wherein a largest individual percentage gear stage stepoccurs between a third largest sprocket of the plurality of sprocketsand a fourth largest sprocket of the plurality of sprockets and betweenthe fourth largest sprocket and a fifth largest sprocket of theplurality of sprockets.
 10. A rear wheel sprocket arrangement accordingto claim 1, wherein a largest sprocket of the plurality of sprockets hasat least forty-four (44) teeth.
 11. A rear wheel sprocket arrangementaccording to claim 10, wherein the largest sprocket has at leastforty-eight (48) teeth.
 12. A rear wheel sprocket arrangement accordingto claim 10, wherein a smallest sprocket of the plurality of sprocketshas at least ten (10) teeth and not more than thirteen (13) teeth.
 13. Arear wheel sprocket arrangement according to claim 12, wherein thesmallest sprocket has at least eleven (11) teeth and not more thanthirteen (13) teeth.
 14. A rear wheel sprocket arrangement according toclaim 1, wherein the number of teeth of each of four (4) largestsprockets of the plurality of sprockets is an integral multiple of four(4).
 15. A rear wheel sprocket arrangement according to claim 14,wherein the number of teeth of each of the four (4) largest sprockets ofthe plurality of sprockets is an integral multiple of eight (8).
 16. Arear wheel sprocket arrangement according to claim 14, wherein thenumber of teeth of each of three (3) sprockets from a group of four (4)axially successive sprockets, comprising the sprockets from a fourthlargest sprocket to a seventh largest sprocket, is an integral multipleof three (3).
 17. A rear wheel sprocket arrangement according to claim1, wherein a largest sprocket of the plurality of sprockets is generallyplanar.
 18. A rear wheel sprocket arrangement according to claim 1,wherein a largest sprocket of the plurality of sprockets has a centralopening through which a driver passes, wherein there is no directform-fitting engagement between the largest sprocket and the driver fortransmitting torque from the largest sprocket to the driver.
 19. A rearwheel sprocket arrangement according to claim 18, wherein the largestsprocket is coupled to the driver by an adapter element for thetransmission of torque, wherein the adapter element is placed on a sideof the largest sprocket which faces away from the rest of the pluralityof sprockets.
 20. A rear wheel sprocket arrangement according to claim1, wherein at least three (3) sprockets are designed as a single-piecesprocket component within the rear wheel sprocket arrangement.
 21. Arear wheel sprocket arrangement according to claim 20, wherein at leastfour (4) sprockets of the plurality of sprockets are designed as thesingle-piece sprocket component within the rear wheel sprocketarrangement.
 22. A rear wheel sprocket arrangement according to claim20, wherein largest and smallest sprockets of the plurality of sprocketsare each formed separately as individual sprockets.
 23. A rear wheelsprocket arrangement according to claim 20, wherein the single-piecesprocket component comprises a second largest sprocket.
 24. A rear wheelsprocket arrangement according to claim 1, wherein the plurality ofsprockets comprises only seven (7) sprockets.
 25. A rear wheel sprocketarrangement according to claim 1, wherein the plurality of sprocketscomprises only eight (8) sprockets.
 26. A rear wheel sprocketarrangement according to claim 1, wherein the plurality of sprocketscomprises only nine (9) sprockets.
 27. A rear wheel sprocket arrangementaccording to claim 1, wherein a front face distance between axiallydirectly adjacent sprockets is between 4.2 millimeters and 4.4millimeters.
 28. A rear wheel sprocket arrangement according to claim27, wherein the front face distance between axially directly adjacentsprockets is between 4.3 millimeters and 4.4 millimeters.
 29. A driveassembly for a bicycle, comprising a rear wheel sprocket arrangementaccording to claim 1, and a front chainring, wherein the number of teethof the front chainring is smaller than the number of teeth of a largestsprocket of the plurality of sprockets and larger than the number ofteeth of a third largest sprocket of the plurality of sprockets.
 30. Adrive assembly for a bicycle according to claim 29, wherein the frontchainring and a second largest sprocket of the plurality of sprocketshave the same number of teeth.
 31. A drive assembly for a bicycleaccording to claim 29, further comprising an assisting electric motorconfigured to transmit assisting torque to the rear wheel via the rearwheel sprocket arrangement, wherein the assisting electric motor iscoupled to the chainring in order to transmit torque.